Neutral Nitrogen in Damped Lyman a Systems

Abstract

Nitrogen abundance determinations in high-redshift galaxies are an important tool for understanding the first stages of galactic chemical evolution. The most intense NI lines, i.e. the triplets at rest wavelengths 1134Å and 1200Å, fall in the optical range for z _abs ≳ 2 and can be observed at high spectral resolution in Damped Lyman α (DLA) systems, where nitrogen is expected to be mainly in neutral form. In practice, only a very few detections have been obtained until now due to the difficulty of disentangling these lines from the Lyman alpha forest in the spectrum of the background QSO. Here we present a new NI detection in a DLA, namely the system at z _abs =3.025 towards QSO 0347–383. An overview of the available nitrogen measurements in DLA systems shows a dispersion of the N/O ratios which suggests that this class of QSO absorbers include objects with different chemical evolution histories.